This invention pertains to a dual valve assembly that allows both air filling and automatic pressure adjustment of a tire.
Currently most filling stations are partially or totally "self-serve" and there is a growing need for a valve that may be permanently installed on a tire that will allow the normal car owner to fill the tire with air and have the air pressure automatically adjust for proper tire inflation. Since different pressures are recommended for different vehicles, such a valve or set of valves would necessarily be made for different pressure ratings or would have a pressure adjustment.
My invention fulfills this need. The invention in its simplified form involves a primary valve with a spring loaded return inside a secondary valve which is held closed with a calibrated control pressure spring. This dual valve assembly threads onto the normal valve stem of a tire in one embodiment. In another embodiment it becomes part of the valve stem.
When the dual valve assembly is screwed on a valve stem, a collar containing a depressor spring under the dual valve assembly partially depresses the valve core valve when the assembly makes a pressure tight seal with the end of the valve stem. At this point the primary valve is opened in the normal way by the projection in the end of the air nozzle in the service station air hose. Both this primary valve and the valve in the valve core are then open. When the tire appears sufficiently inflated the user lifts the air hose filling nozzle from the valve stem and if the pressure inside the tire is high enough, the spring holding the secondary valve closed starts to depress and air then flows outward past the secondary valve to the atmosphere. The user adds air until this venting occurs. The venting continues until the pressure inside the tire falls sufficiently to allow the secondary valve to seat at the calibrated or adjusted spring pressure. The primary valve which seats in the secondary will be closed because of the pressure return spring and pressure within the tire.
In a second embodiment of the invention, the cap containing the dual valve assembly is itself fitted with a second cap that is used to adjust the compression of the spring in the secondary valve and thereby the final air pressure in the tire.
In a third embodiment the dual valve assembly is internally contained in a valve stem. This embodiment usually would have a spring pressure adjusting cap that threads into the top of the valve stem. This embodiment is meant for installation as original equipment or when a tire is changed. In this embodiment as well as the second embodiment the location of the cap in the threads may be marked to indicate compression of the secondary valve spring and thereby final pressure in the tire. The cap may be positioned at the factory for desired pressure or may be adjusted by the user.
This invention then covers a dual valve assembly that may be contained in a cap that screws on existing valve stems or may be an internal part of a valve stem. When the tire is filled with air in a normal way the secondary valve in the assembly will automatically allow air to flow outward through the valve stem until a preset internal pressure within the tire is obtained.